Nuts and Volts

3 were requested at 10 mS intervals. If it’s good enough for Windows, it’s good enough for us. Here’s the PIC32MX timer code:

//***********************************************
//* INITIALIZE THE IN REPORT TIMER
//***********************************************
void InitializeTimer(void)
{
T4CON = 0x0; //Stop and Init Timer
T4CON = 0x0050; //prescaler = 1:32 -
 //internal clock
 //Clear timer register
 //Load period register -
 //0.010 second period
TMR4 = 0;
PR4 = 0x61A8;

IPC4SET = 0x00000005;

// Set priority
//level=1

IFS0bits.T4IF = 0;
IEC0bits.T4IE = 1;

T4CONSET = 0x8000;

//Start Timer
}

The PR4 period register value is calculated as follows:

Timer Clock = 80 MHz
Prescaler = 1:32
Desired Interval = 0.010 seconds
PR4 =

1 raw timer tick time = 1/80000000 = 0.000000012
seconds
1 prescaled timer tick time = 32 0.000000012 =
0.000000400 seconds
PR4 = 0.010 / 0.000000400 = 25000 = 0x61A8

Every 10 mS, Timer4 will overflow and generate an interrupt. The interrupt handler’s job is to place the PIC32MX application in the proper state to retrieve a report from the DualShock 3. The Timer4 interrupt handler looks like this:

//*******************************************
//* IN REPORT TIMER INTERRUPT HANDLER
//*******************************************
#pragma interrupt _T4Interrupt ipl4 vector 16
void _T4Interrupt( void )
{
if (IFS0bits.T4IF)
{
IFS0bits.T4IF = 0;
//mPORTAToggleBits(BIT_0);
if(READY_TO_TX_RX_REPORT == PS3State)
{
PS3State = GET_INPUT_REPORT;

}
}
}

Digilent chipKIT Max32 chipKIT Network Shield www.digilentinc.com Microchip XC32 C Compiler Microchip USB Stack www.microchip.com Ellisys Ellisys USB Explorer 200 Protocol Analyzer www.ellisys.com Sony PlayStation DualShock 3 Controller www.sony.com

58

June 2013

I used the mPORTAToggleBits(BIT_0) function to toggle the RA0 I/O pin. If you want to check my math, uncomment the toggle bit function and put a scope to RA0. As they say, numbers don’t lie.

TAKEOFF ROLL

The PIC32MX is supported by a number of libraries that are designed to help the programmer get the most out of the 32-bit silicon. With that, the first thing we will do is code in some PIC32MX functions that will maximize the microcontroller’s performance. The next bit of coding will kick off the PIC32MX timing mechanisms and interrupt engine. Finally, we will fire up the UART and set it up to run at 115200 bps. All of this startup code can be found in the init() function:

//*******************************************
//* INITIALIZE FUNCTION
//*******************************************
void init(void)
 {
int  value;

value = SYSTEMConfigWaitStatesAndPB(
GetSystemClock() );

// Enable the cache for the best performance
CheKseg0CacheOn();
// Enable Interrupts
INTEnableSystemMultiVectoredInt();
// Wait for PLL lock to stabilize
value = OSCCON;
while (!(value & 0x00000020))
{
value = OSCCON;
}
// Uncomment next 2 lines to check 10 mS
//timer on RA0
//mJTAGPortEnable(DEBUG_JTAGPORT_OFF);
//mPORTASetPinsDigitalOut(BIT_0);

//Initialize UART
setbuf(stdout,NULL); //UART1 REDIRECT
UARTConfigure(UART1, UART_ENABLE_PINS_
TX_RX_ONLY);
UARTSetFifoMode(UART1, UART_INTERRUPT_
ON_TX_NOT_FULL | UART_INTERRUPT_ON_
RX_NOT_EMPTY);
UARTSetLineControl(UART1, UART_DATA_
SIZE_8_BITS | UART_PARITY_NONE |
UART_STOP_BITS_1);
UARTSetDataRate(UART1, GetPeripheral
Clock(), 115200);
UARTEnable(UART1, UART_ENABLE_FLAGS
(UART_PERIPHERAL | UART_RX | UART_TX));